At which wavelength does DNA primarily absorb UV light?

DNA primarily absorbs UV light at a wavelength of 260 nm due to the presence of its aromatic bases, namely adenine, thymine, guanine, and cytosine. These bases contain π (pi) electrons that can engage in electronic transitions when exposed to UV light. The energy from the UV light at this specific wavelength is just right to excite these electrons to a higher energy state, resulting in a maximum absorbance peak. This property is widely used in biochemistry to quantify DNA concentration in a sample using spectrophotometry.

The absorbance at 260 nm is particularly significant because it allows researchers to evaluate the purity of DNA as well; for instance, the ratio of absorbance at 260 nm to that at 280 nm can indicate the presence of proteins, which also absorb UV light but at 280 nm. Thus, 260 nm is a key wavelength for assessing nucleic acids in various laboratory applications.